Japanese Patent Application Laid-Open No. 2005-239711 (Patent Document 1) states as follows:
“The progress in the study of regulatory factors of angiogenesis has led to therapeutic applications of these factors. Among those factors known to promote angiogenesis are vascular endothelial growth factor (VEGF), basic fibroblast growth factor (bFGF) and hepatocyte growth factor (HGF). These growth factors and their genes are now being used to treat diseases that require improvement in the blood circulation (such as arteriosclerosis obliterance and ischemic heart diseases).
However, these growth factors are proteins and are therefore difficult to administer orally. They also pose other problems regarding anaphylactic responses caused by repeated administration, safety of viral vectors used in gene therapies, and side effects such as edema. Hence, there is a need for the development of new treatments.”
Certain diseases are known to be caused by an organic disorder associated with neurite retraction and loss of synapses, though their etiology may vary from disease to disease. Such diseases include Alzheimer's disease, multi-infarct dementia, cerebrovascular dementia, senile dementia, Lewy body disease, Parkinson's disease and Huntington's disease.
Central nerve injuries such as cerebral hemorrhage, cerebral infarction, brain tumor, head injury and spinal cord injury can also be caused by an organic disorder associated with neurite retraction and loss of synapses.
Different medicines for these diseases have been developed that act to protect neurons by different mechanisms.
None of these medicines provide a fundamental treatment for these diseases and are less than satisfactory though they may delay the progress of the disease to some extent. In particular, there is no effective treatment for cerebral infarction that is currently used worldwide other than tissue plasminogen activator (tPA).
Although several medicines currently under development are designed to act to protect neurons, none of them are directed to actively promoting the recovery of nerve function after cerebral infarction.
Regeneration of neural stem cells has attracted much attention and many studies are being conducted in an effort to implant the cells. As far as the treatment of cerebral infarction is concerned; however, the implanted neural stem cells fail to serve as neurons to form neural networks since the neural stem cells have a small chance of survival after implantation or they may not differentiate into neurons.
Recent studies suggest that vascular remodeling such as angiogenesis is essential to the generation and regeneration, as well as to the following differentiation and maturation of neural stem cells and other cells following cerebral infarction (Non-Patent Document 1: J. Clin. Invest.: 114, 2004). Thus, an effective treatment for cerebral infarction is required not only to provide direct protection of neurons to prevent the progress of neuronal damage, but also to promote axonal outgrowth required for regeneration/remodeling of vascular networks and reconstruction of new neural networks in the damaged ischemic penumbra (Non-Patent Document 2: Science, 3:272 (5262), p 664-666 (1996)).
Under such circumstances, a low-molecular-weight compound that can act to promote axonal outgrowth and promote angiogenesis and that can be orally administered is considered a potential drug effective in reducing or treating central nerve injuries such as head injury and spinal cord injury, cerebral infarction, ischemic heart diseases such as myocardial infarction and organic angina, peripheral arterial occlusive diseases such as critical limb ischemia, and after-effects of these diseases, as well as other diseases against which such a compound is considered effective. Such a compound is also considered a potential drug effective in reducing or treating symptoms resulting from a functional or organic disorder of the brain, including cerebral ischemic injuries, such as after-effects of cerebral infarction, cerebral hemorrhage and cerebral arteriosclerosis, as well as diseases associated with an organic disorder resulting from senile dementia, Alzheimer's disease, Parkinson's disease, and after-effects of brain injury, spinal cord injuries and brain surgery.
It is believed that the above-described compound that can promote angiogenesis would effectively act in occluded lesions found in peripheral arterial occlusive diseases, such as arteriosclerosis obliterance, Buerger's disease and Raynaud's disease. It is considered that the compound is particularly effective against critical limb ischemia and other severe symptoms against which conventional medications have no effect.    Patent Document 1: Japanese Patent Laid-Open Publication No. 2005-239711    Non-Patent Document 1: A. Taguchi, et al., J. Clin. Invest., 114:3, p 330-338 (2004)    Non-Patent Document 2: M. Barinaga, Science, 3:272 (5262), p 664-666 (1996)